1. Field of the Invention
The present invention generally relates to magnetic tape cassettes and, more particularly, is directed to a magnetic tape cassette which can be applied to a digital audio tape recorder using a rotary head (i.e. R-DAT).
2. Description of the Prior Art
A digital audio tape recorder has been proposed so far, in which an analog signal such as an audio signal or the like is converted to a digital signal and this digital signal is recorded on and/or reproduced from a magnetic tape. As such digital audio tape recorder, the R-DAT is proposed, which utilizes a rotary head to provide a high recording density.
In the magnetic tape cassette used in the high density recording, if a magnetic tape is smudged by oily components such as fingerprints and dusts or the like, a drop-out occurs in a reproduced signal. Therefore, in order to avoid the occurrence of such drop-out, the magnetic tape must be shielded within the magnetic tape cassette.
An arrangement of a magnetic tape cassette of a shield type for the DAT will be explained with reference to FIGS. 1 to 4.
As illustrated, a magnetic tape cassette represented by reference numeral 1 includes a cassette casing 2, and the cassette casing 2 is formed by fastening an upper half or upper part 3 and a lower half or lower part 4 by some suitable means such as screws or the like. A pair of reel shaft insertion apertures 5 are bored through the lower part 4, and a pair of reel hubs 7 around which a magnetic tape 6 is wound are rotatably supported in the pair of reel shaft insertion apertures 5. The magnetic tape 6 wound around the reel hubs 7 is extended between left and right tape guides 8 provided at the lower half 4 and is exposed to a front. surface opening portion 9 of the cassette casing 2.
At the front portion of the lower part 4, a loading pocket portion 10 is formed, and this pocket portion 10 has a recess portion of U-letter configuration formed at its portion corresponding to the rear side of the magnetic tape 6 exposed to the front opening portion 9. When this magnetic tape cassette is loaded onto a magnetic recording and reproducing apparatus (not shown), a tape loading guide member on the apparatus side enters this pocket portion 10 and withdraws the magnetic tape 6 to the front of the cassette casing 2 (so-called tape loading is performed).
A transparent window portion 11 is formed on the upper part 3, and the user can visually confirm the tape volume of this magnetic tape 6 wound around the reel hubs 7 via this transparent window portion 11. A front lid 12 which opens and closes the front surface opening portion 9 of the cassette casing 2 is attached to the front end portion of the upper half 3 so that it can be pivoted in the vertical direction. When the magnetic tape cassette 1 is not in use, the front surface opening portion 9, i.e. the magnetic tape exposed portion is covered by the front lid 12. When this magnetic tape cassette is loaded onto the magnetic recording and reproducing apparatus, the front lid 12 is pivoted upwards in the vertical direction by a mechanism on the apparatus side, thereby the magnetic tape 6 being uncovered and exposed to the outside.
Further, as shown in FIG. 3, a hub lock member 13 is assembled within the cassette casing 2 so as to inhibit the left and right reel hubs 7 from being rotated uselessly when the magnetic tape cassette is not in use.
The hub lock member 13 is provided with engaging protrusions 13a which correspond with engaging slits 7a formed around the outer peripheral portions of the reel hubs 7. The hub lock member 13 is always spring-biased in the locking direction by a hub lock spring 14 secured to a spring securing portion 13b provided at the central portion of hub lock member 13. The hub lock spring 14 might be formed of a torsion spring. More specifically, the hub lock spring 14 extends its two ends in a substantially inverted V-letter configuration and two ends 14a of the hub lock spring 14 are brought in contact with a front wall 3a of the upper part 3, whereby the hub lock member 13 is always spring-biased in the rear direction, i.e. in the direction in which the engaging protrusions 13a are engaged with the engaging slits 7a of the reel hubs 7. Thus, the reel hubs 7 are locked so as not to rotate when the magnetic tape cassette 1 is not in use.
When the magnetic tape cassette 1 is loaded onto the magnetic recording and reproducing apparatus and the front lid 12 is opened upwardly and rotated as described above, rear end portions 12a of two side surfaces of the front lid 12 are brought in contact with and in engagement with engaging portions 13c elongated to the front portions of the two end portions of the hub lock member 13 to thereby withdraw the engaging portions 13c Therefore, the hub lock member 13 is moved in the frontward direction, i.e. in the direction in which the engaging protrusions 13a are disengaged from the engaging slits 7a of the reel hubs 7 while spring-biasing the torsion spring 14 in its opening direction, thus releasing the reel hubs 7 from their locked conditions.
The hub lock member 13 is assembled within the cassette casing 2 at the same time when the upper and lower parts 3 and 4 are fastened together under the condition such that the hub lock member 13 is slidably engaged on the upper part 3 in the front to back direction beforehand in the assembly process of the magnetic tape cassette. An engaging structure in which the hub lock member 13 is engaged with the upper part 3 will be explained hereinafter. Rectangular openings 15 long in the front to back direction are bored through the left and right portions of the hub lock member 13 and the hub lock member 13 attached to the upper part 3 by caulking pins 16 formed on the inner surface side of the upper part 3 within the rectangular openings 15. Therefore, the hub lock member 13 is slidably moved along the inner surface of the upper part 3 in the front to back direction.
A sliding member or slider 17 is attached to the bottom surface of the lower part 4 of the cassette casing 2 so as to become slidable in the front to back direction. When the magnetic tape cassette is not in use, the slider 17 is located at the front closing position and covers the pocket portion 10 and the reel shaft insertion apertures 5 of the lower part 4. Further, when the magnetic tape cassette is loaded onto the magnetic recording and reproducing apparatus, the slider 17 is slidably moved to the rear opening position by a mechanism of the magnetic recording and reproducing apparatus side, whereby the pocket portion 10 and the reel shaft insertion apertures 5 of the lower part 4 are uncovered.
A slider locking mechanism is provided between the slider 17 and the lower half 4 to hold the slider 17 in the locked condition at the front closing position and at the rear opening position. More specifically, as shown in FIG. 2, this slider locking mechanism is comprised of left and right slider lock members 18 which are formed on one portion of the lower part 4 so as to be vibratory in the vertical to lower direction and front and back engaging apertures 19a and 19b bored through the slider 17 in correspondence with the slider lock members 18. Under the condition that engaging convex portions 18a formed on the tops of the slider lock members 18 are engaged with the rear engaging apertures 19b, the slider 17 is locked at the front closing position, while under the condition that the engaging convex portions 18a of the slider lock members 18 are engaged with the front engaging apertures 19a, the slider 17 is locked at the rear opening position. The slider 17 locked by the slider locking members 18 is released from its locked condition by a releasing member (not shown) provided at the magnetic recording and reproducing apparatus side.
Limiter pins 20 are protruded on the inner side surface of the upper part 3 in correspondence with the slider lock members 18, and the top surfaces of the limiter pins 20 are opposed to the inner surface sides of the top portions of the slider locking members 18 with a predetermined spacing. The limiter pins 20 restrict the amount in which the slider lock members 18 are vibrated with resiliency, or the limiter pins 20 can prevent the slider lock members 18 from being vibrated and deformed more than is necessary, thereby being prevented from being damaged.
In the conventional DAT tape cassette thus constructed, the slider 17 is locked only by the resiliency of the slider lock member 18 so that, because the slider 17 is opened and/or closed repeatedly or due to aging change, the engaging force of the slider lock member 18 is weakened, resulting in the locked condition of the slider 17 being loosened.
To remove this disadvantage, a magnetic tape cassette is proposed, in which a coil spring is additionally interposed between the upper part 3 and the top portion of the slider lock member 18 and a lock holding force applied to the slider 17 by the slider lock member 18 is reinforced by the resilient force of this coil spring (see Japanese Patent Laid-Open Gazette No. 62-79573).
However, in the case of this conventional magnetic tape cassette, the slider locking coil spring is additionally incorporated in addition to the ordinary arrangement, which increases the number of assembly parts. In addition, the assembly work for assembling the very small coil spring is very complicated, which provides a complicated assembly process of a magnetic tape cassette and an expensive magnetic tape cassette.